Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identical oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a formal charge of negative one, where each oxygen carries a − charge while the nitrogen carries a +1 charge, and is commonly used as an example of resonance. Like the isoelectronic carbonate ion, the nitrate ion can be represented by resonance structures: Almost all inorganic nitrate salts are soluble in water at standard temperature and pressure. In organic chemistry a nitrate (not to be confused with nitro) is a functional group with general chemical formula RONO2 where R stands for any organic residue. They are the esters of nitric acid and alcohols formed by nitroxylation. Examples are methyl nitrate ' formed by reaction of methanol and nitric acid, the nitrate of tartaric acid, and the inappropriately named nitroglycerin. Related materials Nitrates should not be confused with nitrites, (NO ) the salts of nitrous acid. Organic compounds containing the nitro functional group (which has the same formula and structure as the nitrate ion save that one of the O− atoms is replaced by thegroup) are known as nitro compounds. Human toxicity Nitrate toxicosis in humans occurs through enterohepatic metabolism of nitrates to ammonia, with nitrite being an intermediate . Nitrites oxidize the iron atoms in hemoglobin from ferrous iron (2+) to ferric iron (3+), rendering it unable to carry oxygen . This process can lead to generalized lack of oxygen in organ tissue and a dangerous condition called methemoglobinemia. Methemoglobinemia can be treated with methylene blue, which reduces ferric iron (3+) in affected blood cells back to ferrous iron (2+). Infants in particular are especially vulnerable to methemoglobinemia due to nitrate metabolizing triglycerides present at higher concentrations than at other stages of development. Methemoglobinemia in infants is colloquially know as "blue baby syndrome". Initial exposure is most often caused by high levels of nitrates in drinking water. However nitrate exposure may also occur if eating for instance vegetables containing high levels of nitrate. Lettuce may contain elevated nitrates under growth conditions such as reduced sunlight, undersupply of the essential micronutrients molybdenum (Mo) and iron (Fe), or high concentrations of nitrate due to reduced assimilation of nitrate in the plant. High levels of nitrate fertilization also contribute to elevated levels of nitrate in the harvested plant .Marschner H 1999 Mineral nutrition of higher plants. Academic Press, London. 889 Some adults can be more susceptible to the effects of nitrates than others. The methemoglobin reductase enzyme may be under-produced or absent in certain people who have an inherited mutationWashington State Department of Health. "Nitrate in Drinking Water." Accessed: September 2, 2009. Available from http://www.doh.wa.gov/ehp/dw/Programs/nitrate.htm. Such individuals cannot break down methemoglobin as rapidly as those who do have the enzyme, leading to increased circulating levels of methemoglobin (the implication being that their blood is not as oxygen-rich). Those with insufficient stomach acidWashington State Department of Health. "Nitrate in Drinking Water." Accessed: September 2, 2009. Available from http://www.doh.wa.gov/ehp/dw/Programs/nitrate.htm (including some vegetarians and vegans) may also be at risk. Ironically, the increased consumption of green, leafy vegetables that typically accompanies these types of diets may lead to increased nitrate intake. A wide variety of medical conditions, including food allergies, asthmaWebMD. "GERD and Asthma." Accessed: September 2, 2009. Available from http://www.webmd.com/asthma/guide/heartburn-asthma, hepatitis, and gallstones may be linked with low stomach acid; these individuals may also be highly sensitive to the effects of nitrates. Marine toxicity .]] In freshwater or estuarine systems close to land, nitrate can reach high levels that can potentially cause the death of fish. While nitrate is much less toxic than ammonia or nitrite,Romano, N.; Zeng, C. (2007). "Acute toxicity of sodium nitrate, potassium nitrate and potassium chloride and their effects on the hemolymph composition and gill structure of early juvenile blue swimmer crabs (''Portunus pelagicus, Linneaus 1758) (Decapoda, Brachyura, Portunidae)." Environmental Toxicology and Chemistry '''26: 1955–1962. levels over 30 ppm of nitrate can inhibit growth, impair the immune system and cause stress in some aquatic species.Nitrates in the Aquarium However, in light of inherent problems with past protocols on acute nitrate toxicity experiments, the extent of nitrate toxicity has been the subject of recent debate. In most cases of excess nitrate concentrations in aquatic systems, the primary source is surface runoff from agricultural or landscaped areas which have received excess nitrate fertilizer. These levels of nitrate can also lead to algae blooms, and when nutrients become limiting (such as potassium, phosphate or nitrate) then eutrophication can occur. As well as leading to water anoxia and dead zones, these blooms may cause other changes to ecosystem function, favouring some groups of organisms over others. Consequently, as nitrates form a component of total dissolved solids, they are widely used as an indicator of water quality. Nitrates are also a by-product of septic systems. Specifically, they are a naturally occurring chemical that is left after the breakdown or decomposition of animal or human waste. Water quality may also be affected through ground water resources that have a high number of septic systems in a watershed. Septics leach down into ground water resources or aquifers and supply nearby bodies of water. Lakes that rely on ground water are often affected by nitrification through this process. See also * Ammonium * f-ratio * Nitrification * Peroxynitrate * Nitrate overview: External links * ATSDR - Case Studies in Environmental Medicine - Nitrate/Nitrite Toxicity References Category:Oxoanions Category:Nitrates Category:Nitrogen metabolism Category:Curing agents Category:Garde manger Category:Water quality indicators Category:Functional groups Category:Non-coordinating anions bs:Nitrat br:Nitrat bg:Нитрат ca:Nitrat cs:Dusičnany da:Nitrat de:Nitrate es:Nitrato eo:Nitrato fr:Nitrate gl:Nitrato ko:질산염 hr:Nitrat it:Nitrato he:חנקה ms:Nitrat nl:Nitraat ja:硝酸塩 no:Nitrat nn:Nitrat pl:Azotany pt:Nitrato ru:Селитра sq:Nitrati simple:Nitrate sk:Dusičnan sl:Nitrat sr:Нитрат sh:Nitrat fi:Nitraatti sv:Nitrat th:ไนเตรต tr:Nitrat zh:硝酸盐